The present invention relates to an apparatus for processing gas by an electron beam (electron beam gas processing apparatus) and more particularly to an electron beam gas processing apparatus suitable for performing the processing of removing/reducing harmful substances in gas, for example, NOx and SOx contained in an exhaust gas.
In order to process a gas exhausted from a thermal power plant, an electron beam gas processing apparatus for performing the process of desulfurization/denitration of the exhaust gas has hitherto been used. The electron beam gas processing apparatus has three vacuum chambers with differential pumping disposed in a reaction room serving as an atmospheric gas room into which an exhaust gas representing an object to be processed is guided or admitted, an electron beam chamber disposed adjacently to an outer differentially pumped chamber, and an electron beam source for irradiating an electron beam to the interior of the electron beam chamber through a draw-out electrode, whereby the electron beam generated from the electron beam source is irradiated on the exhaust gas in the reaction room through the draw-out electrode, electron beam chamber and individual differentially pumped chambers. The exhaust gas in the electron beam chamber and each of the differentially pumped chambers is evacuated by a vacuum pump such as a rotary pump and a constant degree of vacuum is maintained inside the respective chambers. A magnetic lens is disposed in each differentially pumped chamber in order that the electron beam guided to each differentially pumped chamber is focused by each magnetic lens so as to be focused on a designated position in the reaction room. By maintaining the degree of vacuum in the electron beam chamber and individual differentially pumped chambers at a designated value, the locus of the electron beam can be kept to be straight. Further, by changing the current of a filament arranged in the electron beam source, the current value of an arc power supply for generating an arc discharge in the electron beam source or the gas pressure inside the electron beam source or by changing the accelerating voltage applied to the accelerating electrode, the intensity of the electron beam can be adjusted.
In the conventional technique, by virtue of the provision of the plurality of differentially pumped chambers, the beam diameter of the electron beam can be increased but the vacuum pump must be provided in association with each differentially pumped chamber, thus making the construction complicated. Further, the magnetic lens in each differentially pumped chamber is fixedly disposed and therefore, when the filament current, arc current or gas pressure is changed or the accelerating voltage of the electron beam is changed in order to increase the beam current, the degree of focusing of the electron beam is changed and the electron beam cannot be guided to the designated position inside the reaction room. In addition, the electron beam generated from the electron beam chamber is irradiated in the form of a collimated beam and therefore, when a number of electron beams are desired to be irradiated, the electron beam source is forced to be increased in scale.